In nephrology, the conundrum regarding vascular access choice continues
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“Vascular access is the Achilles’ heel of dialysis therapy.”
That is an often-quoted statement in dialysis access literature. Ideal vascular access has eluded us ever since the advent of chronic hemodialysis therapy.
The evolution of various approaches to access management, from the “Fistula First Breakthrough Initiative” to “Fistula First, Catheter Last” and now to “Right Access at the Right Time for the Right Patient for the Right Reasons” summarizes the predicament faced by the vascular access community. Evidence-based medicine continues to dodge many questions on vascular access while the latest guidelines advocate personalized medicine.
Therapeutic advancements have focused on fistula creation and maturation while maintenance of the established access has taken a step back in recent years. The continued reliance on unstandardized monitoring methodologies for access care will hasten access loss and conversion.
Access options
The arteriovenous fistula continues to be promoted as the access of preference and shows superior performance compared with other access choices. In the recently published paper by Nicholas S. Roetker, PhD, MS, and colleagues, patency loss was higher for patients with kidney failure who used an arteriovenous graft compared with patients using an AVF.
“The results suggest that, among patients with a functioning permanent access, arteriovenous fistulas have superior patency compared to arteriovenous grafts, particularly in terms of [primary] assisted patency and secondary patency,” Roetker and colleagues wrote in Kidney Medicine.
The prevalence of AVFs in hemodialysis units is a quality metric for payment and performance ratings developed by CMS, which will continue to preserve “fistula creation in all patients” approach. The access choices are influenced by low rates of infection among patients with AVFs and better patency of functional fistula compared with AVG.
However, the AVF is not perfect. Primary fistula failure continues to be at an unacceptable rate. The Hemodialysis Fistula Maturation cohort study is a multicenter prospective NIH/ National Institute of Diabetes, and Digestive and Kidney Diseases study performed to identify factors associated with AVF maturation. It has provided valuable insights into various biochemical and vascular characteristics determining fistula maturation.
In a recently published analysis from the cohort, researchers reported a primary unassisted maturation rate of 29% of AVFs at 3 months in patients with kidney failure and only a 10% maturation among patients with chronic kidney disease. Nearly one-third of fistulas require some degree of intervention before being termed mature.
Patency
The definition of maturation has evolved from “anatomic” to “functional.” Multiple processes of care and complications are associated with AVF maturation outcomes. Medicare vascular access costs can be two to three times higher for patients whose fistula experiences patency loss and four times higher for patients who never used their fistula.
There is a critical need for a comprehensive risk stratification system based on patient characteristics to guide access selection. Advances in endovascular fistula creation offer an exciting opportunity to broaden the specialties involved in fistula creation. The major hurdles in comprehensive adaptations of these novel devices include cost, the need for trained personnel, adjunctive procedures like coiling, and increased dependency on skilled dialysis personnel for cannulation.
Role of AVGs
In the coming years, advances in graft materials, particularly bioengineered grafts, will make AVGs a valuable option. The significant limitations are a high rate of patency loss compared with the functioning fistula, requiring frequent interventions resulting in higher infection risks.
It is worth noting that grafts are generally implanted in patients who lack suitable veins for a fistula, who have exhausted sites for fistula placement, and as a catheter-sparing strategy. Various studies have reported lower patency rates for grafts treated with angioplasty as the primary intervention.
Using an endovascular stent to treat vein graft anastomosis stenosis has improved patency rates compared with angioplasty alone.
A 2-year randomized single-center study to compare patency rates, number of interventions and cost-effectiveness among angioplasty, deployment of a stent, or use of a stent graft in the treatment of failing AVGs due to restenosis in the venous anastomosis or the outflow vein reported improved patency with the stent graft group without translating into long-term significant cost savings. The settling in of the fistula as the access of choice provides an opportunity for a well-designed randomized trial comparing primary fistula creation to primary graft implantation to answer the question of the best access option.
Relevance of surveillance
The faltering approach with preferred access options, fistula creation and maturation reinforces the need to maintain functioning accesses. Conversion from permanent vascular access to a catheter increases mortality by 80%. Saving and strengthening what you have needs to be prioritized.
Monitoring and surveillance received a new roadmap in the latest Kidney Disease Outcomes Quality Initiative vascular access guidelines. Stenosis-mediated dysfunction were differentiated from other problems, like aneurysms with a new terminology of “access flow dysfunction.”
On the other hand, monitoring strategies were promoted over surveillance to identify dysfunctional access. Monitoring was tasked with identifying stenosis-induced dysfunctional access, while surveillance strategies were expected to improve access outcomes.
While this expectation is logical, prevalent surveillance strategies were initially developed to identify stenosis and dysfunctional access. On its own, surveillance strategies do not change the trajectory of access outcomes. The treatment of stenosis with either balloon angioplasty, stent graft or surgical revisions determines the patency, hence the long-term access outcome.
Surveillance
Monitoring strategy is inherently the weakest link in access care. Monitoring is based on evidence accrued among patients referred to angiographic studies due to a clinical symptom. Data on its effectiveness are lacking when employed by a pool of nonphysician care providers, like dialysis technicians and nurses in a setting where the study cohort comprises both clinically asymptomatic and symptomatic accesses.
Additionally, monitoring relies on the workforce, which was crippled during the ongoing global pandemic. Surveillance strategies require specialized equipment or devices, some of which have low workforce involvement with advanced automation. The reliability and reproducibility of surveillance are frequently questioned but repeated measurements and trending results largely negate the weaknesses.
We have recently published our work using the Vasc-Alert Scoring System, a risk-stratification algorithm (score from 1-10) based on Vasc-Alert access surveillance technology. The high-score cohort (8-10) was not only significantly associated with stenosis but also identified stenosis in 21% of patients with no positive clinical monitoring findings. The high score was sensitive and specific and had excellent negative predictive value, implying that if there is not a high score, then the likelihood of a culprit stenosis causing an access dysfunction is low.
A data-driven, practical surveillance program would aim to decrease staff dependence with the added benefit of lower staff burnout. Few other data-driven, machine-learning surveillance programs are now being evaluated to reinforce monitoring strategies.
Vascular access continues to be a problem with one step forward and two steps back. Thoughtful large-scale randomized studies to address the question of the “ideal” access and optimal access care are needed. In the interim, a personalized access option based on patient characteristics and the best success in avoiding a catheter should be the cornerstone of the decision-making process.
- References:
- Allon M, et al. Am J Kidney Dis. 2018;doi:10.1053/j.ajkd.2017.10.027.
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- Lalathaksha Kumbar, MD, is a clinical associate professor of medicine at Michigan State University College of Human Medicine and section head of interventional nephrology in the division of nephrology and hypertension at Henry Ford Hospital in Detroit. He can be reached at lkumbar1@hfhs.org.
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